Date: Sun, 3 Jan 2016 10:23:43 -0800
From: Robert Harmon <k6uj@pacbell.net>
To: towertalk@contesting.com
Subject: [TowerTalk] Force 12 loading coils
I found this interesting article (below) on the evolution of Force 12's
current Tornado loading coil design from
the beginning with the Tom Schiller, N6BT original design to their final
Tornado version. I put this post on the EHAM antenna reflector but no
interest yet.
I was surprised that in the last part of the article they say that they
wont disclose the Q of their new Tornado coil. Huh ???
Reading thru the article it indicates they went away from Tom's original
design to a smaller dia, smaller inductor,
loading coil design, and now they have gone to their new Tornado design
which looks very similar to Tom's
original design. hmmmmmmmm
I have surmised from this that they developed a piece of #### loading
coil, then went back to a slight variation,
original design, higher Q, more efficient coil they named Tornado. It
bugs me that they wont divulge the Q,
my guess is that they dont want us to compare the Q's of the loading
coil evolution from Tom's original design
to the current Tornado. I think we know why they dont want us to
compare :-)
Anyway I am trying to figure out the Q of the different coils.
here is the article:
http://www.force12inc.com/content/Application%20Note%20-%2040m%20Delta%20Coils%20Overview%20DRAFT%202.pdf
73,
Bob
K6UJ
## No rocket science here. 1/4 inch Al tubing with air , or the newer method,
with the seco spacing strips, is far better than
10 ga magnet wire wound on grooved ABS.
## Q of the coil is just XL / ESR. Calculating XL is easy, its just XL=
2 pi x fl. Measuring or calculating ESR is more of a trick, even
when a HP Q meter is used...or k6sti coil software is used. I replaced the
oem F12 LL rods, made from 3/16 inch solid rods on my F12 340N...with 3/8
inch silver plated
copper tubing coils. ESR works out to aprx .07 ohm per coil. Q works out
to aprx 1760. IF you say double the uh of the coil, you will also
double its ESR..and you will also double its XL...... and Q will not change.
(Since Q = XL / ESR) .
## I had seco systems custom make me an 80D tornado drive for my F-12
EF-180B rotary dipole. I replaced the oem LL 12 ga alumoweld wires
with 16 ft T bar capacity hats. The balance of the loading is done with the
tornado drive.... which is just a pair of 6-12 uh compressible coils. With
coils
fully compressed, they are 12 uh each. When fully expanded, they are 6 uh
each. They are plastic coated copper tubing, 1/4 inch diam, so when mashed
tight, they do not short between turns. Seco can make coils with either cu
or al, and both can be plastic coated if you want.
## per the software etc, there is a big advantage of using copper vs al. A
.375 inch od copper tubing coil would have to be aprx .642 inch od if al
was used instead.
The closest thing to that would be 5/8 inch al tubing.
## If 1/4 inch copper tubing used..... the eq in al tubing would be aprx
.428 inch.
## winding anything on grooved abs plastic will reduce the Q..... higher
esr. I used 3/8 inch silver plated tubing on the 40m els.....since its
readily available and
easy to silver plate. Each coil is small, like aprx 2.8 uh, so its not a
big deal to fabricate. 3/8 inch tubing, once flattened, will easily handle a
1/4-20 SS bolt.
## ken at JK ants, uses 1/4 inch SOLID al for his 40m coils..... then
welds em, where they pass through the al stand offs. Slick method of
constructing his coils.
## last I heard, even the old F12 was using STYRENE covers for its 3/8 inch
AL tubing coils used on its sigma 2 el 80m yagis. I can see where the
covers would
work with heavy snow or ice present, but note they really are not required in
most cases. Optibeam doesn’t use coil covers. The seco systems motor driven
coils
all use covers, to protect the internal motor driven assy.
## 10 ga magnet wire wound on grooved abs, would not be a high Q assy.... way
worse than airdux using the same gauge.
Skin depth on 40m is less than 80m..... so 40m coils should be bigger diam than
typ used on 80m,
like 41% bigger diam material used. Bear in mind that copper is aprx 2%
heavier than steel.....and steel is aprx 2.76 X heavier than AL.
## Check this out. http://www.qsl.net/ve6wz/coil.htm and
http://www.qsl.net/ve6wz/CC_coil.html The Cushcraft XM240 12 ga magnet
wire coils wound on solid
fiberglass only have a Q of 81..which is piss poor. 10 ga would be slightly
better.
Jim VE7RF
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